Rapidly rotating neutron stars with realistic nuclear matter equation of state

TL;DR

This paper compares three numerical methods for modeling rapidly rotating neutron stars with realistic nuclear matter equations of state, highlighting differences in their accuracy at high rotation rates.

Contribution

It provides a detailed comparison of static, slow-rotation, and full Einstein equation solutions for neutron stars with hybrid matter EOS, emphasizing the limitations of slow-rotation approximations.

Findings

The codes agree well at low rotation speeds.

Differences increase exponentially at high rotation rates.

Maximum mass configuration shows a 6.67% discrepancy at Keplerian frequency.

Abstract

We performed a comparison of three different numerical codes for constructing equilibrium models; (I) a code for static equilibrium configurations, (II) an implementation of the Hartle--Thorne slow-rotation approximation, (III) a numerical solution of the full Einstein equations by \texttt{LORENE}. We aimed to construct sequences of uniformly rotating configurations at various rotation frequencies up to the Keplerian frequency for a hybrid hadronic--quark matter EOS where a smooth transition is provided between two separate phases. We investigated the difference of between the results computed by the implementation of Hartle--Thorne slow-rotation approximation and by \texttt{LORENE/nrotstar}, respectively. We have conclude that the codes can the difference between the slow rotating and the fast-rotating approach increase exponentially, reaching 6.67% for the maximal mass configuration rotating at the Keplerian frequency.